I. Field of Invention
This invention applies to the field of systems and/or various apparatus which are used to inspect and measure surface topology and properties of materials. Such systems are used to measure the variations in surface roughness and to detect the presence of cracks and surface flaws with high spatial resolution. The field also encompasses optical characterization methods and apparatus.
II. Background of the Invention
Conventional scanning surface inspection systems currently use optical scattering techniques which are limited in their application because they use light scattering to measure surface topology. The system being proposed herein is based on the measurement of a small electrical potential difference which appears on any solid body when subjected to illumination by a modulated laser light. This voltage is proportional to the induced change in the surface electrical charge and is capacitively measured on various materials such as conductors, semiconductors, ceramics, dielectrics and biological objects. Experiments are easily repeated, and the amplitude of the detected signal depends on the type of material under investigation, and on the surface properties of the sample.
The design of a measuring system capable of performing photocharge voltage measurements for microscopic characterization of material surfaces is here described. Since the measured quantity, the photocharge voltage (PV) is observed on any kind of material present at the surface of the sample under investigation, e.g. semiconductor, insulator and metal, PV measurements can be easily used to evaluate any morphological variation or discontinuity at the surface, as well as in any spatial variation of the surface charge in a uniform semiconductor area.
The spatial variation of PV can be used to evaluate the surface conditions of the sample even with metalization and the variation of the PV due to the monochromatic bias light are used to characterize the surface states.
The proposed technique is completely contactless and it can be used in a high resolution microscope system. In fact, applications are numerous, from thin film and surface mechanical characterization to in-line nondestructive characterization of semiconductor wafers during the various stages of integrated circuits fabrication.